Add missing pad_token_id config property

Fix error:

handler: 'pad_token_id'
traceback: Traceback (most recent call last):
File "/usr/local/lib/python3.10/dist-packages/runpod/serverless/modules/job.py", line 141, in run_job_generator
for output_partial in job_output:
File "/data/handler.py", line 107, in inference
generator, default_settings = load_model()
File "/data/handler.py", line 45, in load_model
config = ExLlamaConfig(model_config_path) # create config from config.json
File "/data/exllama/model.py", line 52, in __init__
self.pad_token_id = read_config["pad_token_id"]
KeyError: 'pad_token_id'

config.json

@@ -22,5 +22,6 @@
   "torch_dtype": "float16",
   "transformers_version": "4.33.0.dev0",
   "use_cache": false,
-  "vocab_size": 32000
+  "vocab_size": 32000,
+  "pad_token_id": 0
 }